Device for generating electrical oscillations



` Ag. 20, 19 57 M 2,803,778

DEVICE FOR GENERATING ELECTRICAL OSCILLATIONS Filed May 19, 1954 2Sheets-Sheet 2 FF f .31

lflllll IN VE N TOR AGENT United States Patent O DEVICE FOR GENERATINGELECTRICAL OSCILLATIONS Gesins Diemer, Eindhoven, Netherlands, assignor,by

mesne assignments, to North American Philips Company, Inc., New York, N.Y., a Corporation of Dela- Ware Application May 19, 1954, Serial No.430,964

Claims priority, application Netherlands March 6, 1947 8 Claims. (CI.SIS-5.12)

This application is a continuation in part of my application Serial No.8,345 filed February 14, 1948 now abandoned.

The invention relates to devices for generating electrical oscillationsof a wavelength of a few centimetres by means of an electric dischargetube, wherein the electrons emanating from the cathode are projectedthrough one or more apertures in an anode on a secondary-emissionelectrode arranged so as to be parallel to the anode and to dischargetubes for use in such devices.

It is already known to generate oscillations of very high frequency bymeans of a tube as described above. The primary electrons are projectedsubstantially perpendicularly on the secondary emisson electrode whichconstitutes the rear wall of a cavity resonator. The anode forms thefront Wall oi the cavity resonator.

The highest frequency at which such a tube can oscillate as a dyratron,i. e. on the negative internal resistance of the secondary-emissionelectrode, is determined by the path to be covered by the secondaryelectrons between the secondary-emission electrode and the anode and bythe voltage difference between the two electrodes, it being assumed thatthe electrons do not oscillate about the parts of the anode but arecollected directly. In such a dynatron the transit time of the secondaryelectrons must be small compared with the period of the alternatingvoltages to be produced.

It has been found in practice that the frequercy cannot exceedapproximately 2000 mes. (wavelength 15 Cms). This occurs with ananode-secondary-cmisson electrode spacing of 1 mm. and with a voltagedifference of 1000 V. between the two electrodes. By raising the voltageand reducing the spacing the wavelength limit may be slightly loweredbut in this case the technical difficulties (flashover) are so great andthe efficiency is so low that in the wavelength range below 10 cns. nosatisfactory results can be obtained. Furthermore, at these wavelengthsat which such a tube still oscillates the eificiency, with normalspacing and field strength, is already comparatively low (by experimentshas been attained at 20 Cms.) since, in order to obtain a suflicientlynegative internal resstance the voltage on the secondary-emissionelectrode must be chosen to be low whereas, in order to obtain shorttransit times the anode voltage must be high. The voltage Swing whichthe sccondary-emission electrode may thus obtain, is consequentlycomparatively small.

With tubes of this kind the negative internal resistance is determinedby the variation of the secondary-emission coeicient with the voltage onthe secondcry-emission electrode At a voltage of some hundreds of voltsat the most this Variation is still suflicient for the most usualsubstances (the variation is greatest at a voltage of 0 v.).

The invention has for its object to obviate the disadvantages of theknown devices, among others the high field strength between the anodeand the secondary-emission electrode and the low efciency.

In a device according to the invention for producing electricaloscillations of a wavelength of a few centimetres in which the electronsemitted from the cathode are projected through one or more apertures inan anode on a secondary-emission electrode parallel to the anode, theseelectrons are concentrated into one or more beams which have smallaperture angles and the axes of which are at an angle of about 45 withthe plane of the anode, the voltages on the anode and thesecondary-emission electrode and their relative spacing being so chosenthat, in the absence of alternating voltages on the electrodes, theprimary electrons still just fall upon the sccondaryemission electrodeand the transit time of the secondary electrons to the anode isapproximately a full period of the oscillations to be produced.

In the device thus obtained the negative internal resistance of thesecondary-emssion electrode is determined by the variation of theprimary current to the sccondaryemission electrode with the voltage onthe latter, whereas, as long as the primary current does not becomeexcessively high, the variation of the sccondary-emission coeicient withvoltage hardly has any influence. With the known devices, in which theprimary electrons fall almost perpendicularly upon thesecondary-emission electrode, the voltage on the lattcr electrode haspractically no influence on the primary current. In a device accordingto the invention the value of the negative internal resistance is alsodetermined by the aperture angles of the electron beams. With anaperture angle of about 5 (the axis of the beam being at an angle ofabout 45 with the anode) the voltage path of the secondary-emissionelectrode in which the whole of the primary current is taken over fromthe anode is approximately of the voltage dillerence between the anodeand the secondary-emission electrode. In order to obtain a great currentbetween the anode and the secondary-emission electrode, the voltage maybe chosen to be such that the secondary-emission coeflicient hasapproximately its maximum value. Initially the efficency increases withthe magnitude of the take-over path, and hence with the aperture angleot the beam. With an excessively large aperture angle the negativeinternal resistance attains a value such that, due to losses of theresistances of the circuit, the eificiency again decreases. The ratiobetween the voltage on the secondary-emission electrode and that on theanode is chosen to be substantialiy equal to the square of the Sine ofthe angle which the electron beam makes With the anode plane, whilst thespacing between the two electrodes is determined in this case by thedesired transit time.

As stated above the axis of the electron beam is at an angie of 45 withrespect to the plane of the anode. However, without any objection thisangle may also be comprised between Zt) and '/0. The aperture angle ofthe electron beam is determined by the size of the cathode and thedistance from an anode and by the diverging eifect of the interveningspace between the anode and the secondary-emission electrode. A value of15 to 20 of the apex of the conical beam directed towards the anodeyields excellent results. The transit time of the secondary electronsmay, in general, vary between a half and one and a half periods of theoscillations to be produced, with which the tube still continues tooscillate. It is thus possible to tune over a large wavelength rangewithout modifying the voltage.

The simplest Construction or' a tube for use in a device according tothe invention is that in which only one primary electron beam is used.In this case the anode and the secondary-emission electrode may have theform of more or less fiat discs, which are directly sealed into a glasswall of the tube and thus incorporated in a cavity resonator.

A favourable form of a tube for use in a device according to theinvention is that in which use is made of two cathodes arranged oueither side of the axis of the system &803378 and the secondary-emissionelectrode is divided into two halves, each of which co-operates with oneof the two electron beams. The two halves of the secondary-emissionelectrode may, in this case, consist of the bent ends of a Lecher linepassing through the wall of the tube in the form of two fiat strips. Thetube is then adapted to operate in push-pun, so that the efficiency isvery high.

The invention is going to be explained more tully with reference to theaccompanying drawing, in which Fig. 1 represents a tube with a singleelectron beam and Fig. 2 a tube having two electron beams and a dividedsecondaryemission electrode. Fig. 3 represents a tube according to theinvention incorporated in an oscillating circuit.

Referring to Fig. l, 1 designates the glass wall or envelope of thetube, 2 the anode constituted by a copper disc, 4 the secondary-emissionelectrode. the bent part 5 of which is in the shape of a truncated coneand is located at a distance of 1.5 mms. from the anode 2 and oppositethe aperturc 3 provided in the latter. The hollow cathode 6 is arrangedin such manner that a beam emanating therefrom and projected, throughthe aperture in the anode, on the part 5 of the secondary-emissionelectrode is at an angle of about 45 with the *anode plane. In front ofthe anode and the cathode are provided concentrating members 7 and 8respectively, to the first of which a separate voltage may be applied.Into the bottom of the tube are sealed a plurality of supply wires 9,whilst on top of the secondary-emission electrode another glass wall 10is sealed to permit the secondary-emission electrode to be cooled in asimple manner by means of a liquid. A further advantage of the obliquelyincident primary beam is that the seconda'y electrons have to travel ina space comprised between two fiat plates, so that the transit timedispersion is very small. Associated with the tube is a toroidal cavityresonator 31 coupled galvanically with the anode 2 and capacitivelythrough a mica ring 32 with the secondary emissive electrode 5 acoupling loop 33 serves the purpose of guiding out the energy generated.

Referring to Fig. 2, 11 designates the glass wall of the tube in whichan anode 12 having an aperture 19 is provided. Two cathodes 13 and 14are 'arranged on either side of the axis of the anode in such mannerthat the junction lines between the centre of the aperture 19 and thecentres of the cathodes are at an angle of 45 with the plane of theanode. In front of the two cathodes are arranged concentrating members15 and 16 whilst in front of the aperture in the anode two concentratingmembers 17 and 18 are arranged which are formed as solid bodies ofrevolution. The members 17 and 18 each have the form of two superimposedfrustums of cones and are each revolved about an axis, perpendicular tothe surface of the respective cathodes, and passing through the centrethereof. into the wall of the tube are sealed two Lecher wire strips 34and 35 which terminate in sections 20 and 21 parallel to the anode. Thelatter sections are coated with caesiurn oxide to serve assecondary-emission electrodes. The electrons emanating from the cathode13 are projected on the part 21 of the secondary-emission electrode andthose emanating from the cathode 14 on the secondary-emission electrode20. If the voltage on the anode is 1400 v. and that on thesecondary-emission electrode 800 v oscillations may be produced in awavelength range of from 3 to 5 cms. with an efliciency of approximately20% at a wavelength of 5 cms. The dimensions of the tube may be computedfrom a scale shown at the side of the latter, said scale beingcalibrated in mms. The two electrodes 20 and 21 are connected to aLecher wire system consisting of the strips 34 and 35, which are tunedwith the aid of a tuning bridge 36.

Fig. 3 shows a tube according to Fig. 1 with associated resonator in agenerating circuit. The anode voltage s derived from a battery 37 andthe secondary emssive electrode is tapped about midway between thecathode and anode. The concentrating electrode 7 is tapped at 38 4 at aslightly positive or negative voltage with respect to cathode 6. Theheater battery is indicated at 39.

What is claimed is:

1. An electric discharge device for generating short wavelengthelectrical oscillations comprising an electron discharge tube, said tubeincluding an anode electrode having a planar surface and provided withan aperture, a secondary-emissive electrode mounted on one side of saidanode and spaccd therefrom a given distance, means mounted on the otherside of said anode to generate a small aperturc angle electron beamforming an angle between 20 to 70 with the surface of said anode anddirected towards said aperture, means for applying potentials to saidanode and secondary-emissive electrode at which the transit time ofsecondary electrons liberated by the electron beam and travelling fromthe secondarr emissive electrode to the anode is about one full periodof the electrical oscillations and at which the electrons produced bythe generating means just strike the secondary-emissive electrode in theabsence of signal potentials on the electrode& and a resonant circuitassociated with the space between the anode and the secondary-emissiveelectrode and adapted to be excited into oscillation by the electronflow.

2. An electric discharge device for generating short wavelengthelectrical oscillations comprising an electron discharge tube, said tubeincluding an anode electrode having a planar surface and provided withan aperture, a secondary-emissive electrode mounted on one side of saidanode and having a plan-ar surface portion which is parallel to theanode planar surface and spaced therefrom a given distance, meansmounted on the other side of said anode to generate a smallaperture-angle electron beam forming an angle of about 45 with thesurface of said anode and directed towards said ape'ture, means for applying potcntials to said anode and secondary-emissive electrode atwhich the transit time of secondary electrons liberated by the electronheam and travelling from the seconda'y-emissive eiectrode to the anodeis about one full period of the electrical oscillations and at which theelectrons produced by the generating means just strike thesecondary-emissive electrode in the absence of signal potentials on theelectrodcs, and a resonant circuit associatcd with the Space between theanode and the secondaryemissive electrode and adapted to be excited intooscilia tion by the electron flow.

3. An electron discharge tube as claimed in claim 6 in which saidsecondary-emissive electrode has a body portion in the form of atruncated cone.

4. An electron discharge tube as claimed in claim 7 in which saidsecondary-emissive electrode has a body portion in the form of atruncated cone mounted on one side of said anode in spaced relationshipto said anode with the apex directed towards the anode.

5. An electron discharge tube comprising an anode electrode having aplanar surface and provided with an aperture, a first secondary-emissiveelectrode arranged on one side of said anode a first cathode sourcemounted on the other side of said anode diametrically opposite saidfirst secondary-emissive electrode for generating a beam of electronsdirected toward s said aperturc and said first emissive electrode, asecond secondarycmissive electrode located on the same side of saidanode as the first secondary emissive electrode, a second cathode sourcear ranged on the same side of the anode as the first cathode source anddiametrically opposed to said second second ary-emissive electrode forgenerating a beam of electrons directed towards said aperture and saidsecond secondaryetnissive electrode, each of said electron beams formingan angle of approximately 45 with said anode and also forming an angleof approximately therebetweeu, each of said first and second cathodcsources subtending an angle of approximately l5 with said aperture.

6. An electron discharge tube as claimed in claim 7 in which saidsecondary-emissivc electrode has a body portion in the form of atruncated cone mounted on one side of said anode in spaced relationshipto said anode with the apex directed towards the anode, and said meansto generate a small aperturc-angle electron beam comprses a cathodesource mounted on the other side of said anode, said cathode sourcesubtending an angle of approximately 15 with said aperture, a firstconcentrating electrode in the form of a frustum of a cone with its apexin the direction of said cathode source and having a voltage appliedthereto and in aligned spaced relation with said cathode forconcentrating said electron beam, and a second concentrating electrodepositioned between said first concentrating electrode and said anode andaligned with said aperture in said anode and having an offset aperturealigned with said first concentrating electrode, said secondconcentrating electrode having a voltage applied thereto forconcentrating said electron beam.

7. An electron discharge tube comprising an anode electrode having aplanar surface and provided with an aperture, a first secondary-emissiveelectrode arranged on one side of said anode, a first cathode sourcearranged on the other side of said anode diametrically opposite saidfirst secondary-emissive electrode for generating a beam of electrons asdirected towards said aperture and said first secondary-emissiveelectrode, a second secondary-emissve electrode located on the same sideof said anode as the first seconda'y-emissve electrode, a second cathodesource arranged on the same side of the anode as the first cathode anddiametrically opposed to said second secondaryemissive electrode forgenerating a beam of electrons directed towards said aperture and saidsecond secondaryemissive electrode, each of said electron beams formingan angle of 45 With said anode and also forming an angle ofapproximately 90" therebetween, each of said first and second cathodesources also subtending an angle of ap proximately 15" with saidaperture, a first concentrating electrode having the form of a truncatedcone and in spaced relation with said first cathode, a secondconcentrating electrode positioned between said first concentratngelectrode and said anode, a third concentrating electrode also havingthe form of a truncated cone and in spaced relation with said secondcathode, and a fourth concentrating electrode positoned between saidthird concentrating electrode and said anode.

8. An electric discharge device for generating short wavelengthelectrical oscillations comprising an eiectron discharge tube, said tubeincluding an anode electrode having a planar surface and provided withan aperture, a Lecher line mounted on one side of said anode, said linebeing constituted by a pair of flat strips each having bent ends facingsaid anode and spaced therefrom a given distance, asecondary-electron-emissive material on said bent ends, firstelectron-beam generating means mounted on the other side of said anodediametrcally opposite one of said bent ends for generating an electronbeam directed towards said aperture and said one bent end, secondelectron-beam generating means mounted on the same side of the anode onthe first generating means and diametrically opposite the other of saidbent ends for generating an electron beam directed towards said apertureand said other bent end, each of said electron beams forming an angle ofapproximately with said anode, each of said generating means subtendinga small angle with said aperture, and means for applying potentials tosaid Lecher line and said anode at which the transit time of secondaryelectrons liberated by the electron beams and travelling from the bentends to the anode is about one full period of the electricaloscillations and at which the electrons produced by the generating meansjust strike their associated bent ends in the absence of signalpotentials on the Lecher line or electrode.

References Cited in the file of this patent UNITED STATES PATENTS2,128,232 Dallenbach Aug. 30, 1938 2,170,2l9 Seiler Aug. 22, 19392,416,303 Parker Feb. 25, 1947 2,425,748 Llewellyn Aug. 19, 19472,581,408 Hamilton Jan. 8, 1952

